1. Field of the Invention
The present invention relates to a substrate for cell culture capable of transferring cells grown in adhesion culture to a cell sheet, an organ and a protein sheet, etc., while keeping the cells alive, for use in processing of cells and regenerative medicine.
2. Background Art
At present, various types of animal cells and vegetable cells have been cultured and novel cell-culture methods have been developed. Cell-culture technique has been used to elucidate biochemical phenomena and properties of cells and produce useful substances. Furthermore, to check physiological activities and toxicity of artificially synthesized medicaments, the cultured cells are used. Moreover, recently, researchers have intensively studied on regenerative medicine for transplanting cells or tissue cultured by an in vitro cell-culture step, to a patient.
Some types of cells (in particular, most animal cells) are known to grow while anchoring (adhering) to something. Since they have such adhesion dependency, cells cannot survive for a long time in vitro in a floating state. When the cells having the adhesion dependency are cultured, a carrier must be used for attaching the cells. In general, a plastic culture plate uniformly coated with a cell adhesive protein such as collagen or fibronectin is used. These cell adhesive proteins are known to act on cultured cells to facilitate adhesion of the cells and exert an effect upon morphogenesis of the cells.
On the other hand, there is a report on a technique for adhering cultured cells only to a small limited portion of a substrate to align the cells. This technique makes it possible to apply cultured cells to artificial organs, biosensors and bioreactors, etc. Cultured cells are usually aligned by use of a surface-patterned substrate constituted of regions different in cell adhesiveness. When cells are cultured on the surface-patterned substrate, cells adhere only to an adhesive surface, thereby aligning the cells.
For example, JP Patent Publication (Kokai) No. 02-245181A (1990) discloses that cells are cultured by use of a charge retaining medium having an electrostatic pattern formed thereon for proliferating the nerve cells in a circuit form. JP Patent Publication (Kokai) No. 03-7576A (1991) discloses that photolithographic patterning is applied to a substrate formed of a cell-adhesive or non-adhesive photosensitive hydrophilic polymer and cells are cultured on the patterned surface of the substrate to align the cultured cells.
Furthermore, JP Patent Publication (Kokai) No. 05-176753A (1993) discloses a substrate for cell culture having a pattern formed of a substance such as collagen, which influences a cell-adhesion ratio and morphology of cells, and a method of preparing the substrate by photolithography. When cells are cultured on such a substrate, a larger number of cells adhere onto the surface coated with collagen, etc. In this manner, patterning of cells is performed.
However, depending upon the usage thereof, patterns on a substrate for cell culture must be formed with high accuracy. When patterning is photolithographically performed using a photosensitive material as mentioned above, a highly precise pattern can be obtained; however, in this case, a cell adhesive material must have photosensitivity. Unfortunately, it is often difficult to chemically impart photosensitivity to a biopolymer etc. A cell adhesive material must be selected from an extremely narrow range. In addition, in photolithographic method using a photoresist, a developing solution and the like must be used. These solutions sometimes have adverse effects upon cell culture.
Furthermore, to form a precise pattern of a cell adhesive material, a micro-contact printing method is proposed by George M. Whitesides of Harvard University (e.g., U.S. Pat. Nos. 5,512,131 and 5,900,160 and JP Patent Publication (Kokai) Nos. 9-240125A (1997) and 10-12545A (1998). However, it is difficult to industrially apply this method in manufacturing a cell culture substrate having a patterned cell adhesive material.
Recently, a technique for transferring viable cells cultured in accordance with a pattern to tissues and organs and a tissue formed by the technique have been reported (JP Patent Publication (Kokai) No. 2005-342112A and WO 2005/038011). However, this technique has problems. Since it takes a long time to transfer cells, intricate operations are required for maintaining the activity of the cells.